1. Field of the Invention
The present invention relates to packaging of optically interactive electronic devices. More particularly, the present invention relates to a package for a solid-state image sensor and methods for simultaneously assembling a plurality of such packages.
2. State of the Art
Solid-state image sensors, for example, charge coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) chips, are increasingly in demand for incorporation into electronic devices. They may be used for a variety of applications including consumer electronics like digital cameras, cellular telephones and hand-held scanners. Conventionally, these image sensor chips have been packaged within a discrete housing for protection from environmental stresses and to provide electrical communication with other components of the larger electronic device into which they are incorporated. The typical housing is a unitary ceramic or plastic shell having a cavity into which an image sensor chip is mounted. The chip is wire bonded to conductive elements within the cavity, and a window or at least partially optically transparent lid covers the cavity to allow light or other forms of electromagnetic radiation to pass through to sensing circuitry on the active surface of the chip. The transparent lid may also be formed to provide an optical function such as focusing the light or other radiation and/or filtering selected wavelengths thereof. The materials and structure involved with this packaging technique require a fabrication process that can be time consuming, costly and consist of several precision assembly steps. Due to the competitive nature of today's semiconductor industry, even a small reduction in packaging cost would be of great benefit, especially when considered in terms of the high volume of components being manufactured to meet growing demands.
In response to large-scale production requirements, various attempts have been made to simplify the construction of image sensor packaging. U.S. Pat. No. 6,351,027 to Giboney et al. and U.S. Pat. No. 6,285,064 to Foster, for instance, disclose wafer-level packaging formed by laying a solid sidewall piece or an adhesive matrix over a wafer having an array of sensor devices and covering it with a transparent top piece. The wafer is then singulated to create discrete chip-scale packages. While this approach reduces material costs and assembly steps, it does not completely protect the semiconductor chips from the environment and requires attaching material directly to the wafer surface, which could damage the sensor devices. U.S. Pat. No. 6,266,197 to Glenn et al. discloses a method for forming image sensor packages wherein an array of image sensors is wire bonded to a carrier substrate, and a molded window array is placed over the array of image sensors. The substrate and attached molded window array are then singulated to form a plurality of individual image sensor packages. The molded window array of Glenn et al., however, still suffers from the fact that individual transparent windows must be formed within or later attached to the molded array, requiring additional assembly and alignment steps during fabrication. U.S. Pat. No. 5,811,799 to Wu discloses an image sensor package formed by attaching a plurality of preformed or glue walls to an array of printed wiring frames having image sensors thereon and sealing the walls with transparent material. The printed wiring frames are then diced to form discrete packages. Once again, this arrangement may require the attachment or formation of multiple components during fabrication, and the disclosed printed wiring frames have a conductive via output arrangement that may not be suitable for certain high I/O image sensor chips.
As is evident from the foregoing description of the state of the art, what is needed is a simplified method for forming an image sensor package that is conducive to mass production while still offering suitable and robust protection for an image sensor chip.